In recent years, there has been proposed mobile terminals having a function for accessing a server on a network, particularly on the Internet, to obtain information.
Downloading of information to the mobile terminals is accompanied by a variety of services to users, such as video clip/music information delivery, enhanced security in financial or commercial transactions that require the strict confidentiality, and the like.
FIG. 1 is a diagram showing an example of the system configuration for accessing a server S on a network N with the use of a mobile terminal T.
As can be seen in FIG. 1, a gateway G is placed at an access point to the network N from the mobile terminal T.
The gateway G and the mobile terminal T communicate via a wireless communications line. A communications protocol called WAP (Wireless Application Protocol), which is optimized according to characteristics of the wireless communications line and mobile terminal, is applied to the wireless communications line. Besides, communication is established between the server S and the gateway G over a standard protocol on the network N. For example, if the network N is the Internet, an Internet protocol such as HTTP (HyperText Transfer Protocol), TCP (Transmission Control Protocol) or the like is employed.
The gateway G is provided with the protocol conversion function for carrying out the conversion of WAP into the standard protocol on the network N or vice versa. The gateway G also performs the data conversion function. For example, the gateway G converts an HTML document into a WML (Wireless Markup Language) document when the server S stores documents in HTML, or converts a WML document in text format into the one in binary format to compress the data when the server S stores WML documents as text.
In this system, a wide variety of services can be offered. On the other hand, the mobile terminal T cannot completely reject, if any, erroneous programs and malicious modules when downloading. An error or disruptive code in the downloaded program may cause damage to the telephone function of the mobile terminal T.
In order to avoid such malfunction, there is proposed an environment for the mobile terminal, in which the area for implementing basic functions such as the telephone function is separated from the area for storing and executing downloaded programs as shown in FIG. 2.
Even with this environment, however, a failure in the area for the program executing function could harm the basic functions when both the areas are operated in the same OS (Operating System). Therefore, the environment cannot provide perfect protective measures.